This project is designed to study the peripheral vascular control mechanisms presently operable in lower vertebrates. Studies are nearly completed on an example of the Class Elasmobranchii (sharks, skates and rays). This class of primitive creatures, as exemplified by Squalus acanthias, exhibits little or no neurogenic control of the peripheral vascular system although it possesses vascular receptors which respond to autonomically active drugs. It also has the capability of responding to Angiotensin II but the pressor effect is brought about only by the release of catecholamines - a mechanism which is present in mammals, but subservient to Angiotensin receptors which react directly to this polypeptide. This elasmobranch (Squalus acanthias) also can convert Angiotensin I to Angiotensin II enzymatically although it apparently cannot generate renin or Angiotensin I. The study has now moved to amphibia. Recent experiments have indicated that the amphibian peripheral vascular system is highly compliant (similar to that of elasmobranchs), responds to autonomically active drugs but without evidence (to date) of a peripheral neurogenic vascular control system. The bullfrog also reacts to angiotensin with a pressor response but without enthusiasm. Similar studies are planned for teleost fishes and reptiles - probably turtle.